Electron microscopes



Sept; 4, 1956 M. ElsFl-:LDT ELECTRQN MICRoscoPEs Filed ug. 22. 1951 2Sheets-Sheet 1 Flr.

United States Patent ELECTRON MCRUSCOPES Manfred Eisfeldt,Berlin-Tempelhof, Germanyhassiguor to Siemens @a HalskeAktiengesellschaft, Munich, Germany, a corporation of GermanyApplication August 22, 1951, Serial No. 243,070 Claims priority,appiication Germany August 29, 1950 22 Claims. (Cl. 313-84) Thisinvention relates to electron microscopes, and is particularly concernedwith a permanent magnetic electron lens system for such microscopes.

Permanent magnetic electron lens systems are known, comprisingregulating means for adjusting the refractive power of the lenses. Suchregulators are required, for example, for the focusing by changing therefractive power of the objective or tovregulate the nal magnificationby changing the refractive power of the projective.

A prior regulator of this kind employs for the adjustment of themagnetic iux, a regulator nut which is associated with across-sectionally reduced portion of the outer casing surrounding thelenses. If relatively great regulation eiects are to be obtained, it isnecessary to provide a narrow cross-section of the casing so that thetlux may be nearly completely interrupted. The result is a relativelygreat outwardly eiective stray magnetic iield.

Regulators have also been proposed in which a part of the lens pole shoeis axially displaced, making it impossible to provideV for a certainunalterably predetermined form of the pole shoe for all operatingpositions.

In accordance with the invention, there is provided for the adjustmentof the refractive power of the lenses a regulating member which isdisposed within the casing surrounding the pole shoe system and thepermanent magnetic system. The regulator is magnetically connected withone pole of the magnetic system and is adjustable from the outside, andin all regulating positions is in series with the magnetic circuit.

As compared with the initially mentioned prior structures, the new lenssystem is free of an outwardly eective magnetic field, because theassociated regulator does not coact with a cross-sectional defined partof the outer casing, but is completely disposed therein.

The regulator is furthermore a structural element which is entirelyindependent of the pole shoe system of the lenses. The shape of the poleshoe is not changed and is in no way affected by the regulator or by itsoperation.

Several structural forms are possible for carrying out the invention. Aparticularly simple structure is obtained by using an adjustable annularregulating member which is disposed ray-symmetrical, that is,symmetrical with respect to the optical axis. This regulating member maybe provided with teeth for coaction with teeth extending from a part ofthe magnetic system. An annular regulating member without any teeth isused if it is to be disposed for axial displacement.

Other embodiments of the invention contemplate the use of rotatableregulating members. These members, as well as relatively stationarycoacting parts, are provided with magnetically coacting teeth. Thesestructures are indicated in axially short embodiments.

The regulating member and the stationary coacting part may be closelyadjacent or may be in one terminal position in engagement.

The form of the regulator teeth may vary. They may,

T.faterrted Sept.v 4, 1956 ice one-half of the symmetrical structure ofan embodiment comprising four pole shoe lenses of an image-forming orfocusing system of an electron microscope;

Fig. la shows a portion of Fig. 1 and in diagrammatic manner additionaldetails for operating certain parts thereof;

Figs. 2, 3, and 4 illustrate fragmentary views of different forms ofrotatable regulator structures; and

Figs. 5 and 6 show one-half of the symmetrical struc-V ture of anotherembodiment of a lens system according to the invention.

Numeral 1 in Fig. 1 indicates the pole shoes of the objective; 2 and 3are the pole shoes of two intermediate lenses; and 4 indicates the polesh'oes of the projective. The magnetic outer casing of the lens'systemcomprises the two transverse walls or lids 5 and 6 and the cylindricalmember forming the wall 7. The outer pole shoes of the lenses 1 and 4extend directly from the transverse walls 5 and 6. The remaining poleshoes of thelenses are disposed on the tubular parts 8, 9, 10 which formcarriers therefor. The carriers 8 and lllhave annular radially outwardlydirected extensions 11, 12. Between the transverse Wall 5 and theextension 11 is disposed a ring-shaped permanent magnet 13, and asimilar magnet 14 is disposed between the transverse wall 6 and theextension 12. The poles of the two magnets are so disposed that theouter casing comprising the walls. 5, 6, 7 is connected with poles ofthe identical sign.

For the regulation of the objective lens 1, there is proi vided aring-shaped regulating member 15, also shown in Fig. la. Suitable knownmeans Stl'to 57, shown in Fig. la are provided for axially displacingthis member 15 relative to the pole shoe carrier 8 in the directionindiv cated by the double arrow 16. This regulator serves for thefocusing or sharp adjustment of the electron stream forming the specimenimage.

The means for eiecting the displacement of the member 15 from theoutside may comprise suitable guide means or waysalong which the member15 may be moved and the gearing extending therefrom in vacuumtightmanner to the outside and having operating means, for example, a handleor knob 57 (Fig. la) or the like for effecting ythe displacement. Suchoperating means may be constructed generally along the lines of gearingsdisclosed and described, for example, in Patents Nos. 2,215,794 and2,247,524 and in copending application Ser. No. 244,195, led Aug. 29,1951, now Patent No. 2,714,678 dated August 2, 1955.

Between the outer shell wall 7 and the pole shoe carrier 9 is provided arotatable regulator 17 for continuously varying the flux conducted tothe carrier 9 for the purpose of continuously varying the iinal imagemagnication. This regulator may receive different forms'. Three examplesare illustrated in Figs. 2-4 which show the structure in diagrammaticfragmentary views as seen when looking along the sectional line A-A ofFig. l. The means for operating the regulator comprises, as shown inFig. la, an annular inner member 63 having alateral extension 66provided with an external gear meshing with the gear wheel 67, thelatter carryinga pinion 69 meshing with a pinion 68 on a rod 70 whichextends invacuumtight manner through the casing Wall 7 and carries aknob 71. The annular member 63 isV provided with a dovetail disposed inaV guideway in thestationary part 4G. Rota- 10 for securing the poleshoe carriers and associated parts on ythe inside ofthe casing 7.Referring again to the structurefor axially displacing the ,regulatormember is', the screw 5.0; carries a key @which slides in a groove inthe annular rib 11' extending from the pole shoe carrier 8. The serewisthus moved only-axially to displace the member 15.' Numeral 80 indicatesa scale and numeral 81 indicates a pointer rotatable with a knob 71 forindicating on the'scale adjustments etected by the knob.

ln lthe structure shown in Fig. 2, there are provided teeth 18 whichproject radially inwardly from the casing wall 7. The pole shoe carrier9is provided with an annular member disposed rotatable thereon andhaving teeth 19 which extend -therefrom'radially outwardly for coactionwith the teeth i3.l The faces of the teeth 18, 19 are inclined as shown.teeth are in engagement so that the magnetic flux to the pole shoecarrier member 9,.and therefore to the lenses 2 and 3, is at itsgreatest value. vAs a result the refractive power of the lenses andtherewith the final image magnification are greatest. By rotating theannular member carrying the teeth`19 in the direction of the arrow 2t)(Fig. 2), the refractive power will be continuously varied or adjusted,i. e., it will Vbe progressively reduced, thereby progressively reducingthe final image magnification down to a minimal value when the .teethV19 are in the dotted terminal position 21.

The means for effecting from the outside the rotation of theannular-member on the carrier 9 from which extend the teeth 19, mayagain be a'suitable gearing constructed and disposed in vacuumtightrelationship to the lens system, for example, along the teaching of thepreviously mentioned copending application Ser. No. 244,195, now PatentNo. 2,714,678.

The pole shoe carrier 9is disposed in stationary position by a ringlikemember 40, which will be referred to later on. Suitable journal meansfor the annular regulating member carrying the teeth 19 is providedthereon, and this annular regulating member may have a gear for coactionwith a gear wheel on a suitably journalled shaftY which extends invacuumtight manner to the outside through a bushing in oneV of thecasing walls. An operating handle Yor knob or the like may be carried bythe shaft on the outside for effecting the adjustment of the annularregulating member-and therewith of the teeth 19 relative to the teeth18.

Fig. 3 shows an embodiment in which the regulator comprises an annularrotatable member having radially outwardly directed teeth 23 forcoaction with teeth 22 extending radially inwardly from the casing wall7. The coacting faces of the teeth are in this case cut on a cylindricalline which is symmetrical to the path of the electron stream. Thegearing required and the operation resulting therefrom may correspond tothose explained in connection with Fig. 2.

The structure illustrated in Fig. 4 employs a regulator comprising armsor members 25 which are angularly dis- -placeable about pivot means 24extending alongside the l intermediate lenseszandsis -held in positionbyasta- In the'full-line position 'these f .4 tionary ring 40 (Fig. l)of magnetic material which engages the carrier 9 as shown.- The ring 443may be secured in any desirable and suitable manner, for example, bynonmagnetic axially extending annular` spacing rings disposed on eachside thereof and engaging with their other ends the extensions 11 Vand12 of the pole shoe bodies 8 and 11)..

Parts of the 'embodiment shown in Figs. 5 and 6, which are marked bynumerals corresponding to the numerals in Fig. l,indicatefidentical-elements. Identical poles of the permanent magnets31,` 32 are in thisembodiment disposed in engagement with the annularextensions 11 and 12 projecting radially outwardly` from the pole shoecarriers 8`V and 10. .The other polesofthese permanent magnets 31, 32extend axially inwardly for coaction with a rotatable regulator 33,34,35 which is disposed centrally of the pole shoe carrier 9 having thepole shoes for the ltwo lenses 2 and 3.. The regulator 33,-.34-35 serves4the purpose o'f'varying the magnetic Alux to the pole shoe carrier9 forthe purpose of adjusting or regulating the final image magnification.Numerals 36;-37 Vand33-39 indicate two rotatable regulators lforcoaction, respectively with the projective 4 andl with the objective 1.The regulator 38-39 serves forthe focusing, and the regulator 36-37 foradditional `'regulation of theV nal'image magnification.

The means for operating the regulators of Figs. 5 and 6 from theyoutside cor'n'prises suitable known gearing of the typealreadyexplained in vconnection Vwith thedescription of thepreviousgures; t v v It will be appreciated from the examples describedabove, that the inventionpermits construction of a simple and efiicientimage-forming system for electron microscopes comprising fourlenses'which arefexcited by permanent magnets and Yhaving a regulatingmember or deviceV which Vforms a bridge between the outer casingzof 'thelenses and a pole shoe`member which carries the secondl p ole shoe ofthe second lens and the first pole shoe o f the third lens. The examplesshow that the adjustmentsrequired in an electron microscope (focusingand ymagniication) can be eectedin a very simple manner,` resulting infull illumination of the final imagein all operating positions. i Y

The handle portions of theregulators, which are on the outside, arepreferably .provided with or coact with index marksy or suitable scalemeans which may be calibrated, for example, so as :to obtain directreading ofthe nal image magniication. f

-. indicate that the structure provides satisfactoryV possi-` The casingforming the walls S, 6, 7 is preferably made of a plurality of parts.`Thus, as indicated in Fig.V y1 the transverse wall members S and 6 areseparate members,

and the cylindrical wall member 7 is made of two parts suitablyassembled with the transverse .walls 5 and 6 so as to facilitateassembly, adjustments, and also the mag! netization of the unitcomprising the-permanent magnet` system and its coacting pole shoes.

The evacuating holes i1 in Fig 5 have been shown to bilities forevac'uatingV the cathode arearbyV connecting a high-vacuum pump toexhaust the space underneath the last projective. j

The invention is particularly suitable for use4V with electronmicroscopes, but may find uses in other types of apparatus for producingand/ or projecting particle beams.V Changes may be made within the scopeand spirit of the Iappended claims-.which define what isbelieved `newand desired to have'protected by Letters Patent.

Iclaim: Y l. An electron microscope or the like h aVinga-casing andcomprising pole shoe means and permanentuma'gnet means disposed in saidcasing, means for connecting said casing with one pole of said magnetmeans,an adjustable regulator within saidv casing, said regulatorcomprising aV movable member whichris separate from saidperrnan ei itVmagnet means and disposed in a magneticfcircuit in series with said poleshoe means, control means in said casing for moving said movable member,and actuating means extending from said control means to the outside foroperating said control means to move said movable member so as to adjustthe refractive power of said lens system.

2. The structure defined in claim 1, wherein said movable regulatormember is `an annular member carrying teeth the free ends of which arecut on a cylindrical line which is symmetrical to the optical axis, andstationary members for coaction with said teeth.

3. The structure defined in claim 1, wherein said movable regulatormember is an .annular member carrying teeth the free ends of which arecut on a cylindrical line which is symmetrical to the optical axis, anda stationary toothed member forming teeth for coaction with the teeth ofsaid movable regulator member.

4. The structure dened in claim l, wherein said movable member is arotatable member.

5. The structure defined in claim 1, wherein said movable member is anaxially displaceable member.

6. The structure defined in claim 1, comprising a stationary regulatingmember for coaction with said movable regulating member, said stationaryand said movable members being substantially in engagement in oneterminal position of said movable member.

7. The structure defined in claim 1, wherein said movable member is arotatable member carrying a plurality of radially outwardly directedteeth, a plurality of radially stationary inwardly directed teethextending from the wall of said casing for coaction with the teeth ofsaid movable member, the coacting outer faces of said teeth being cut ona cylindrical line which is symmetrical to the optical axis of thestructure.

8. The structure defined in claim l, wherein said movable member is arotatable member carrying a plurality of radially outwardly directedteeth, a plurality of radially stationary inwardly directed teethextending from the wall of said casing for coaction with the teeth ofsaid movable member, the coacting outer faces of said teeth beingangularly inclined to provide for engagement thereof in one terminalposition of said movable member.

9. ln an electron microscope having an image-forming system comprisingfour magnetic lenses and permanent magnet excitation means therefor andhaving a casing for surrounding said lenses and said permanent magnetmeans, a regulator for adjusting the refractive power of said lenssystem, said regulator being disposed inside of said casing Iand forminga bridge extending between said casing and the pole shoe body of saidsystem which carries the second pole shoe of the second lens and the rstpole shoe of the third lens.

10. The structure deined in claim 9, together with a relativelystationary ring-shaped member of magnetic material for securing the poleshoe body of the two intermediate lenses substantially centrallythereof.

11. The structure delined in claim 9, wherein said permanent magnetmeans comprises two cylindrically shaped permanent magnets for theexcitation of all four lenses, one of said magnets being associated withthe objective lens and the other magnet being associated with theprojective lens.

12. The structure deiined in claim 9, together with operating means forsaid regulator, and scale means for said operating means to indicate theadjustment of the regulator in terms of magnication of the final image.

13. In an electron microscope comprising a cylindrical casing, alens-forming pole shoe system and permanent magnet excitation meanstherefor disposed within said casing and completely enveloped thereby, adevice also disposed within said casing for adjusting the refractivepower of said lens system, said device comprising movable adjustingmeans disposed on the outside of said pole shoe means for altering themagnetic flux affecting said pole means, control means for operatingsaid movable adjusting means, yand means extending to the outside ofsaid casing for actuating said control means.

i4. The structure defined in claim 13, wherein said movable adjustingmeans is an annular member which is axially movably disposed on theoutside of said pole shoe means.

15. The structure defined in claim 13, wherein said movable adjustingmeans comprises a plurality of members which extend radially outwardlyfrom said pole shoe means for coaction with similar stationary memberswhich extend radially inwardly from the wall of said casing.

16. The structure defined in claim 13, wherein said movable adjustingmeans comprises an arm which is pivotally secured on the inside of saidcasing, .and means for angularly moving said :arm to adjust the positionof its free end relative to said pole shoe means.

17. The structure dened in vclaim 13, wherein said movable adjustingmeans comprises a plurality of arms which are pivotally disposed on theinside of said casing, 'and means for angularly moving said arms toadjust the free ends thereof relative to said pole shoe means.

18. In an electron microscope, three axially serially disposed annularpole shoe means forming lenses including an objective lens andintermediate lenses and a projective lens, an annular extensionprojecting radially from each of the two pole shoe means forming thelenses for said objective lens and projective lens, respectively, acasing, ring-shaped permanent magnet means connected with each of saidextensions for establishing a magnetic circuit between said objectivelens and projective lens pole shoe means and the inside wall of saidcasing, and a rotatable regulator carried by the pole shoe means formingsaid intermediate lenses for varying the magnetic iiux therefrom to saidcasing.

19. The structure defined in claim 18, together with an axially movableregulator for eecting the magnetic liux of the pole shoe means whichforms the objective lens.

20. The structure dened in claim 18, together with rotatable regulatormeans for varying the magnetic ux in the magnetic circuit from saidpermanent magnet means to said casing.

21. The structure defined in claim 18, wherein said rotatable regulatorcomprises an -annular hub which is rotatable on the corresponding poleshoe means, a plurality of teeth extending radially outwardly from saidhub, and a plurality of coacting teeth extending radially inwardly fromthe inside wall of said casing.

22. The structure defined in claim 18, together with gear means foroperating said rotatable regulator.

References Cited in the le of this patent UNITED STATES PATENTS2,220,973 Marton Nov. 12, 1940 2,305,458 Rusk-a et al. Dec. 15, 19422,305,761 Bor-ries et al. Dec. 22, 1942 2,503,173 Reisner Apr. 4, 19502,533,687 Quam Dec. 12, 1950

